Maximum decimal latitude / longitude?

Question

What is the maximum length (in kilometers or miles, but please indicate) that on the surface of the Earth there can be one degree of latitude and longitude?

I'm not sure if I will be clear enough, let me rephrase that. The earth, as we all know, is not an ideal circle, and a change of 1.0 in latitude / longitude at the equator (or in Ecuador) can mean one distance, while the same change at the poles can mean another completely different distance.

I am trying to reduce the number of results returned by a database (in this case MySQL) so that I can calculate the distances between several points using the Grand Circle . Instead of selecting all the points and then calculating them individually, I want to select the coordinates that are inside the latitude / longitude boundaries, for example:

SELECT * FROM poi WHERE latitude >= 75 AND latitude <= 80 AND longitude >= 75 AND longitude <= 80; 

PS: This is late, and I feel that my English did not fit as I expected, if there is something that you cannot understand, tell me about it and I will fix / improve it as necessary, thanks.

Answer 1

The degree of latitude varies little , from about 110.6 km at the equator to about 111.7 near the poles. If the Earth were an ideal sphere, it would be permanent. For purposes such as obtaining a list of points within 10 km of the known (lat, lon), provided that a constant of 111 km should be in order.

However, this is a completely different story with longitude . It ranges from about 111.3 km at the equator, 55.8 km at 60 degrees latitude, 1.9 km at 89 degrees latitude to zero at the pole.

You asked the wrong question; you need to know MINIMUM length to ensure that your request does not reject valid candidates, and, unfortunately, the minimum length in longitude is ZERO!

Let's say you take other people's councils to use a constant of about 111 km for latitude and longitude. For a 10 km query, you should use a margin of 10/111 = 0.09009 degrees in latitude or longitude. This is normal at the equator. However, at the 60th latitude (where, for example, Stockholm), traveling east at 0.09 degrees longitude, you get only about 5 km. In this case, you incorrectly reject approximately half of the valid answers !

Fortunately, the calculations for obtaining the best longitude boundary (which depends on the latitude of the known point) are very simple - see this answer by SO , and the article by Jan Matushek that he refers.

Answer 2

The initial definition of a nautical mile was the length of one minute of longitude at the equator. Thus, around the equator was 360 * 60 = 21,600 nautical miles. Similarly, the initial definition of kilometer was that 10,000 km = length from the pole to the equator. Therefore, assuming spherical earth, it would be:

• 40,000 ÷ 21,600 = 1.852 km / min.
• 1.852 × 60 = 111.11 km per degree.

Resolution of spheroidal earth instead of spherical will slightly adjust the coefficient, but not so much. You can be sure that the coefficient is less than 1.9 km per minute or 114 km per degree.

Answer 3

If you can use the spatial extensions of MySQL: http://dev.mysql.com/doc/refman/5.0/en/spatial-extensions.html , you can use its operators and functions to filter points and calculate distances, See http://dev.mysql.com/doc/refman/5.0/en/functions-that-test-spatial-relationships-between-geometries.html , in particular the functions contain () and distance () .

Answer 4

The reference ellipsoid used for the Earth is the WGS84 system, which means that the Earth’s radius for the equator is 6,378,137 m or 3,963.19 miles

The maximum longitude is reached at the equator and approximately (upper bound) 111.3195 km or 69.1708 miles

The maximum length of one degree latitude is reached between the equator and 1 °. It is almost exactly equal to the maximum longitude; in a first approximation, it is shown that the difference is less than 4.2 m, which gives

111.3153 km or 69.1682 miles